Runtime linker

[Lana Black]

Hello,

My personal project involves making a port of GHC for an almost bare-bones 
environment, which doesn't provide runtime linking support. GHC configure 
script sets `TargetHasRTSLinker` flag, but it seems to be ignored in RTS 
itself, and the linker is built regardless.

Is this a regression, perhaps due to the migration from Makefiles to Hadrian? 
Or is building RTS without runtime linker no longer supported?

Thank you.